docs: def join(self, name, args, arg_separator=None):
          """implementation details"""
          if None is arg_separator:
              arg_separator = ', '
          args = [_f for _f in args if _f]
  
          if not args:
              args_str = ' '
          elif len(args) == 1:
              args_str = ' ' + args[0] + ' '
          else:
              args_str = ' ' + arg_separator.join(args) + ' '
  
          return ''.join([name, self.__begin, args_str, self.__end])